Cheapest priced copy (Avatar: The Last Airbender Eternal): $5.99 at Card Kingdom, near mint, their price list as of .
Koma, Cosmos Serpent 
Legendary Creature — Serpent · 6/6 · Mythic · Kaldheim · #221
This spell can't be countered.
At the beginning of each upkeep, create a 3/3 blue Serpent creature token named Koma's Coil.
Sacrifice another Serpent: Choose one —
• Tap target permanent. Its activated abilities can't be activated this turn.
• Koma gains indestructible until end of turn.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
7 printings · $5.99 to $22.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Kaldheim | 221 | Mythic | $6.99 | $9.99 |
| Kaldheim | 326 | Mythic | $9.49 | $22.99 |
| Murders at Karlov Manor Commander | 213 | Mythic | $6.99 | — |
| Kaldheim Promos | 221p | Mythic | $7.49 | $11.99 |
| Kaldheim Promos | 221s | Mythic | — | $20.99 |
| Secret Lair Drop | 1765 | Mythic | $18.99 | $21.99 |
| Avatar: The Last Airbender Eternal (The Monstrous Serpent) | 51 | Mythic | $5.99 | $10.99 |
5 rulings from Wizards of the Coast
- 5 February 2021A spell or ability that counters spells can still target Koma, Cosmos Serpent. When that spell or ability resolves, Koma won't be countered, but any additional effects of the countering spell or ability will still happen.
- 5 February 2021The first mode of Koma's activated ability doesn't stop static abilities from affecting the game, and it doesn't stop triggered abilities from triggering. Unlike similar effects, it does stop mana abilities from being activated. Most activated abilities that produce mana as they resolve are mana abilities.
- 5 February 2021If you choose the first mode of Koma's activated ability, you can choose a permanent that's already tapped as the target. The effect stopping its activated abilities will still apply.
- 5 February 2021You can't sacrifice Koma itself to activate its last ability, but you can sacrifice any other Serpent you control, including Koma's Coil.
- 5 February 2021Activated abilities contain a colon and appear in the form "[Cost]: [Effect]." Some keywords such as equip are activated abilities and will have colons in their reminder texts. Loyalty abilities of planeswalkers are also activated abilities.